java.lang.AssertionError
        at org.netbeans.spi.project.support.ant.ProjectProperties$PP.write(ProjectProperties.java:219)
        at org.netbeans.spi.project.support.ant.ProjectProperties.write(ProjectProperties.java:134)
        at org.netbeans.spi.project.support.ant.AntProjectHelper.save(AntProjectHelper.java:595)
        at org.netbeans.spi.project.support.ant.AntProjectHelper.access$100(AntProjectHelper.java:102)
        at org.netbeans.spi.project.support.ant.AntProjectHelper$1.save(AntProjectHelper.java:140)
        at org.netbeans.modules.project.ant.AntBasedProjectFactorySingleton.saveProject(AntBasedProjectFactorySingleton.java:337)
        at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:643)
        at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:632)
        at org.openide.util.Mutex.writeAccess(Mutex.java:433)
        at org.netbeans.api.project.ProjectManager.saveProject(ProjectManager.java:632)
        at org.netbeans.modules.j2ee.sun.ide.j2ee.BuildExtension.abbreviateBuildXml(BuildExtension.java:146)
        at org.netbeans.modules.j2ee.sun.ide.j2ee.ModuleConfigurationImpl$StaticBuildExtensionListener.rewriteBuildImpl(ModuleConfigurationImpl.java:356)
        at org.netbeans.modules.j2ee.sun.ide.j2ee.ModuleConfigurationImpl$StaticBuildExtensionListener.access$100(ModuleConfigurationImpl.java:316)
        at org.netbeans.modules.j2ee.sun.ide.j2ee.ModuleConfigurationImpl$StaticBuildExtensionListener$1.run(ModuleConfigurationImpl.java:412)
        at org.openide.util.Mutex.leaveImpl(Mutex.java:902)
        at org.openide.util.Mutex.leave(Mutex.java:835)
        at org.openide.util.Mutex.readAccess(Mutex.java:287)
        at org.netbeans.spi.project.support.ant.ProjectProperties$PP.fireChange(ProjectProperties.java:339)
        at org.netbeans.spi.project.support.ant.ProjectProperties$PP.diskChange(ProjectProperties.java:358)
        at org.netbeans.spi.project.support.ant.ProjectProperties$PP.fileChanged(ProjectProperties.java:373)
        at org.openide.filesystems.FileUtil$Holder.fileChanged(FileUtil.java:345)
        at org.openide.filesystems.FCLSupport$DispatchEventWrapper.dispatchEventImpl(FCLSupport.java:136)
        at org.openide.filesystems.FCLSupport$DispatchEventWrapper.dispatchEvent(FCLSupport.java:122)
        at org.openide.filesystems.FCLSupport.dispatchEvent(FCLSupport.java:99)
        at org.openide.filesystems.FileObject$ED.dispatch(FileObject.java:1014)
        at org.openide.filesystems.EventControl.invokeDispatchers(EventControl.java:203)
        at org.openide.filesystems.EventControl.exitAtomicAction(EventControl.java:177)
        at org.openide.filesystems.EventControl.runAtomicAction(EventControl.java:122)
        at org.openide.filesystems.FileSystem.runAtomicAction(FileSystem.java:509)
        at org.netbeans.spi.project.support.ant.ProjectProperties$PP.write(ProjectProperties.java:228)
        at org.netbeans.spi.project.support.ant.ProjectProperties.write(ProjectProperties.java:134)
        at org.netbeans.spi.project.support.ant.AntProjectHelper.save(AntProjectHelper.java:595)
        at org.netbeans.spi.project.support.ant.AntProjectHelper.access$100(AntProjectHelper.java:102)
        at org.netbeans.spi.project.support.ant.AntProjectHelper$1.save(AntProjectHelper.java:140)
        at org.netbeans.modules.project.ant.AntBasedProjectFactorySingleton.saveProject(AntBasedProjectFactorySingleton.java:337)
        at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:643)
        at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:632)
        at org.openide.util.Mutex.writeAccess(Mutex.java:433)
        at org.netbeans.api.project.ProjectManager.saveProject(ProjectManager.java:632)
        at org.netbeans.modules.web.project.ui.customizer.WebProjectProperties.save(WebProjectProperties.java:458)
        at org.netbeans.modules.web.project.ui.customizer.CustomizerProviderImpl$StoreListener.actionPerformed(CustomizerProviderImpl.java:177)
        at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2$1.run(CustomizerDialog.java:277)
        at org.openide.util.Mutex.writeAccess(Mutex.java:394)
        at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2.run(CustomizerDialog.java:273)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:573)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1005)